The werewolf.
The metamorphosis of man becoming a wolf (or another animal) is physically impossible.
In the middle ages the believe in Werewolf's was wide spread: the stories and legends about Werewolf's come from Scandinavia, France, Germany, Central- and Eastern Europe, the Balkan and Greece. .
The Werewolf-idea probably has it's origins from the prehistoric hunters who use to wrap themselves in hides, made by the skin of a wolf, because they believed that they would posses the same powers as this feared predator.
The Werewolf legends in which the transformation took place by full moon also descended from the prehistory.
When humans tamed wild dogs for the hunt they must have seen how these animals howled to a full moon.
Throughout the whole social development of mankind, the moon, the hunt and wolfs were connected in more and more myths.
In many legends the goddess of the moon hunts (like the Roman Diane, the Greek Artemis and the Babolonic Ishtar) with her hounds, which are, man transformed into wolfs.
And so was the myth of the Werewolf born. .
Lycanthropy (meaning wolf man) influenced the Werewolf-idea because it was often wrongly seen as a synonym for Werewolf's.
Lycanthropy is an existing psychical illness: the scientist Marcellus Sedates discovered that in the second century after Christ.
Someone who suffers of Lycanthropy believes that he can transform himself into a wolf. Depending on the seriousness of the case, Lycanthropen tear up raw meat with their teeth, howl and scream at the moon and attack other people with a devastating blood-thirst in which they slice the throat of their victim open in an uncontrollable rage.
History is full of these Werewolf stories, the middle ages as peak. This shows due to the fact that there were (only) in France between 1520 and 1630, 30.000 processes about werewolves. In reality the criminals suffered of Lycanthropy and other mental illnesses that can cause cannibalism and serial murders.